The first report of primary hypotonia with abnormal electromyogram and CBS mutation in a Chinese child.

BACKGROUND: Classic Homocystinuria (HCU) is the second most treatable aminoacidopathy. It affects multiple organs in varying degrees, and early recognition and treatment is crucial to improve the prognosis. Mutations in the CBS gene result in classic HCU, the most common form. Genetic testing is important for the accurate diagnosis of this severe disorder. METHOD: Case report. RESULT: A 6-year-old boy presented with high myopia, ectopia lentis, and hypotonia. A brain MRI showed no abnormality, and his electromyogram implicated myogenic damage. His serum homocysteine was 277.5 µmol/L (normal ≤ 15 µmol/L), and methionine was 352.56 µmol/L (normal 0–80 µmol/L); thus, he was diagnosed with classic HCU. Compound heterozygous mutations at two different sites on the cystathionine beta‑synthase (CBS) gene (c.767G > T, c.949 A > G) were identified; the former had not been reported previously. CONCLUSIONS: This study reported a novel mutation of CBS gene (c.767G > T). To our knowledge, this is the first report of this novel clinical manifestation of primary hypotonia in homocystinuria patients.